1. Field of the Invention
The present invention relates to a biochip for testing such substances as DNA, RNA or protein and, in particular, to a biochip that is extremely safe and can reduce the cost of testing.
2. Description of the Prior Art
Methods of testing substances, such as DNA, using biochips have been known well. FIG. 1 is a schematic view showing a conventional system for reading the sequence of a DNA target by scanning a hybridized DNA chip using a biochip reader. The DNA chips shown in FIG. 1, as well as in FIGS. 2 and 3 which are discussed later, are described in “Popular Science”-AUGUST 1999, Times Mirror Magazines, Inc.
In this system, excitation light is radiated at the hybridized DNA chip within biochip 10 and fluorescent light emitted from a fluorescent marker is read using biochip reader 20 so that the sequence of the DNA target, for example, is identified. It should be noted that cartridge 11 is formed using a material that is transparent to the excitation light and fluorescent light.
Biochip 10 in this system is configured in such a manner that substrate 12, on which a multitude of known DNA chips CL are arranged in arrays, is housed within cartridge 11 as shown in FIG. 2. In biochip 10, solution 15 containing target DNA segments previously marked with a fluorescent marker is injected from inlet 13 using solution infusion means 14, such as a pipette, prior to read-out operation, as shown in FIG. 3, so that the DNA segments are hybridized with the probe DNA chip.
On the other hand, such test samples as blood, are sometimes found to be contaminated with a virus such as HIV.
Therefore, there is a growing tendency that for safety reasons, disposable equipment is used for such medical appliances as syringes.
In contrast, the method of introducing a solution shown in FIG. 3 involves the risk of the operator being infected with a virus, such as HIV, as a result of accidental contact with the solution due to mishandling. This risk exists because the method always involves transferring the solution from the solution infusion means 14 or the like to the cartridge 11.
Another problem with the prior art method is that the cost of testing increases since more than one kind of medical equipment must be disposed of, including syringes, appliances used for preprocessing purposes, solution infusion means, DNA chips, and so on.
In the Japanese Laid-open Patent Application 2001-235468 “Biochip,” which is a patent application filed by the inventors mentioned in the application concerned, a biochip that has solved the aforementioned problems and can increase safety and reduce test costs is described. This biochip is configured as shown in FIG. 4.
The biochip comprises blood collection tube 31, instead of a conventional spit tube, which is inserted in a syringe cylinder in order to collect blood. The blood collection tube is formed into a cylindrical shape using a solid material transparent to excitation light and fluorescent light produced. The opening of blood collection tube 31 is sealed with a rubber plug 32 whose middle area is pierced with a needle, and blood collection tube 31 as a whole is kept under negative pressure.
Blood collected through the needle is temporarily retained within collection block 33 and then introduced to preprocessing block 34, where the blood is preprocessed. This preprocessing comprises a series of processes, including separating lymphocytes from the blood, isolating DNA from the separated lymphocytes, and adding a fluorescent marker to the isolated DNA.
Housed in the innermost section of blood collection tube 31 is substrate 35, similar to the one shown in FIG. 1, on which probe DNA segments are arranged in arrays. In the innermost section, DNA segments that infiltrate from preprocessing block 34 and the probe DNA segments are hybridized.
It is understood that such a biochip as discussed above is advantageous in that processes, from blood collection to preprocessing and hybridization, are run consistently and automatically. However, the biochip requires the use of a rigid blood collection tube and is therefore costly. Another problem is that the biochip requires the use of a suction pump in order to keep the blood collection tube under negative pressure, thus resulting in the system as a whole being significantly expensive.